If you mean that each company would insist on making their own that won't talk to the others... Email was actually invented that way.

I don't remember exactly what company (I think it was Novel), but one made a fortune bridging them.

There's nothing wrong with, and possibly better, to start out with a protocol only to support an application. But nowadays the pipeline for graduating into open protocols has broken. We have 15 messaging apps and no interop. Even Facebook and Google Gchat used to support open protocols. That's gone. It's actually much worse than before the internet where telephones were all globally interoperable.